When a substrate such as a semiconductor wafer or a liquid crystal glass is transferred in a fabrication process of semiconductor devices, liquid crystals, or the like, the lower surface of the substrate is attracted to and held by a hand of a robot, and the robot and the hand are moved to transfer the substrate to a next process. This system of attracting the lower surface of the substrate by the hand may cause damage to the lower surface of the substrate or may cause particles to be attached to the lower surface of the substrate at the time of attraction.
There is also a hand for holding an outer peripheral portion of a substrate by dropping the substrate into a concave recess of the hand. However, because it is necessary to provide a clearance (gap) between the outer peripheral portion of the substrate and the concave recess for receiving the substrate, the substrate may be displaced in position or may fall, and thus the substrate cannot be transferred at a high speed.
For the above reasons, an edge-grip hand (referred also as an edge-grip end effector or an edge clamp hand) for gripping an outer peripheral portion of a substrate has recently become mainstream. Japanese Patent Publication No. 4600856 discloses an edge-grip hand whose receiving parts and a gripping part for gripping an edge of a substrate are inclined to grip the substrate only through contact between a portion of the outer peripheral portion of the substrate, and the receiving parts and the gripping part.
However, the edge-grip hand actually has regions where the substrate is brought into sliding contact with the receiving parts and the gripping part, and thus particles are generated from such regions. Generally, the surface, to be processed, of the substrate faces upwardly and the hand is disposed below the substrate, and the receiving parts and the gripping part are also disposed below the outer peripheral portion of the substrate. The substrate transfer space is kept in a downflow condition in many instances. Furthermore, because an area which is a few mm (generally, about 3 mm) wide at the outer peripheral portion of the substrate is not usually used as products, even if particles are generated, they pose no particular problems. Nevertheless, a different situation arises in a wet environment.
FIGS. 16A and 16B are schematic views showing the operation of a general edge-grip hand in a wet environment.
As shown in FIG. 16A, when the hand operates in a wet environment, a liquid such as a cleaning liquid or a rinse liquid is attached to a receiving part 301 and a gripping part 302 of the hand. When the substrate which has been polished is transferred, a polishing liquid (slurry) which has been used in the polishing process is attached to the receiving part 301 and the gripping part 302 of the hand.
As shown in FIG. 16B, when the gripping part 302 is moved to chuck the substrate W between the gripping part 302 and the receiving part 301, the substrate W slides up an inclined surface of the receiving part 301. At this time, the substrate W rubs against the receiving part 301, thus generating particles. The particles are taken into the liquid such as a cleaning liquid or a rinse liquid. As shown in FIG. 16B, as the gripping part 302 and the substrate W move, the liquid flows onto the substrate under inertial forces. Therefore, the substrate W is contaminated everywhere thereof.